Creating Product Mock Ups
The main purpose of a mockup is to show what the GUI will look like and how the user will interact with it. It should be clear from your annotations how the product will be used.
Creating Mockups
Hand Drawings
It is completely fine to have hand drawings as your mockups, but these must be annotated.
Adobe XD
https://www.adobe.com/products/xd/details.html
It provides you with an extensive set of tools to create mockups and user flows. You must download the program if you’d like to use it.
MockFlow
It has more features than Adobe XD but it is limited to 1 project and two collaborators.
Moqups
Similar to MockFlow but can be used directly on a browser without having to download a separate program.